[PATCH] D11724: COFF: Add test for ld/section created import library

Thu Aug 6 09:28:01 PDT 2015

On Thu, Aug 6, 2015 at 9:24 AM, Martell Malone <martellmalone at gmail.com>
wrote:

> On second thought, we don't have to solve that only with the import
>> library. You can create a (regular) COFF object containing a thunk for an
>> aliased function, and include that object file to a .lib, no?
>
> Yes that seems like a good solution to this problem I might be able to add
> something to the genlib tool to support this.
> I might have to mockup one for yaml2obj.
> Can we have a regular coff object in the same lib as an implib ?
>

I believe so -- the import library is just a regular ar file (.lib file)
after all and there's no special bit or something that distinguishes import
libraries and other .lib files, but you may want to try if in doubt. You
can add a regular COFF file to an existing import library using lib command.

>
> On Thu, Aug 6, 2015 at 5:17 PM, Rui Ueyama <ruiu at google.com> wrote:
>
>> On second thought, we don't have to solve that only with the import
>> library. You can create a (regular) COFF object containing a thunk for an
>> aliased function, and include that object file to a .lib, no?
>>
>> On Thu, Aug 6, 2015 at 8:22 AM, Rui Ueyama <ruiu at google.com> wrote:
>>
>>> I don't think the short import library supports that. With that you can
>>> undecorate names, but AFAIK you cannot define arbitrary aliases for
>>> dllexported symbols. Does mingw-w64 heavily relies on that feature?
>>>
>>> On Thu, Aug 6, 2015 at 8:14 AM, Martell Malone <martellmalone at gmail.com>
>>> wrote:
>>>
>>>> Before I let this slip by aswell there is one big issue with switching
>>>> over to the implib format for mingw-w64
>>>>
>>>> LIBRARY "user32.dll"
>>>> EXPORTS
>>>> MessageBoxA == MessageBoxW
>>>>
>>>> dlltool objct format provides us with the option of having an alias.
>>>> Can we do this in implib ?
>>>>
>>>> What the above .def means that where MessagBoxW is called it is joined
>>>> to MessageBoxA.
>>>>
>>>>
>>>> On Thu, Aug 6, 2015 at 3:58 PM, Martell Malone <martellmalone at gmail.com
>>>> > wrote:
>>>>
>>>>> Yeah, I found that too and it (especially the way how it creates a gap
>>>>>> between .idata$3 and .idata$4) looks really hacky. I also found that GNU ld
>>>>>> has a special logic to order .idata$<n> sections.
>>>>>> At first I thought that I could mimic GNU ld and MSVC linker to
>>>>>> generate the .idata section, but seems like it would really mess up the DLL
>>>>>> import table generation code. We probably should keep the existing logic
>>>>>
>>>>> Yeah I don't think copying gnu ld is the way to go, it is a very hacky
>>>>> project to say the least :)
>>>>>
>>>>>
>>>>> It feels to me that it makes more sense to add a new option to dlltool
>>>>>> to generate short import libraries. It shouldn't be that hard. Martell,
>>>>>> what do you think?
>>>>>
>>>>> I already wrote a replacement tool for this called genlib that will go
>>>>> into the mingw-w64 project.
>>>>> I want to remove mingw-w64's dependancy on binutils so that we can
>>>>> have a clang based toolchain without binutils at all.
>>>>> The notion of having dlltool as part of binutils made no sense in the
>>>>> first place, It should have been part of mingw to begin with.
>>>>> The name was chosen to correlate to on of mingw-w64's other tools
>>>>> called gendef which creates the def files from parsing dll's.
>>>>> I'm still finalizing the code in this and doing some tests.
>>>>>
>>>>> I then tried to detect dlltool-style import files and read them as if
>>>>>> they were short import libraries, so that I can keep the existing code.
>>>>>> That didn't work well because it's not easy to detect dlltool-style import
>>>>>> files in a reliable manner without sacrificing performance.
>>>>>
>>>>> While you might not want to merge because of this into the official
>>>>> project because of performance issues it might be something for the
>>>>> mingw-w64 users to avail of until ld supports import style libraries.
>>>>>
>>>>> If you have the patch for this I'd like have a look at it if possible.
>>>>> I'd like to try and apply this over the PECOFF for the clang 3.7
>>>>> package in our msys2 distro.
>>>>>
>>>>> The issue I have is I would have to get approval to switch to using
>>>>> genlib instead of dlltool as mingw-w64's default.
>>>>> This would not be approved until ld supports implibs and the next
>>>>> version of binutils released.
>>>>> As you probably well know how things work that could take months to
>>>>> get changed over.
>>>>> I'd like to use your patch as a base for a temporary stop over until
>>>>> this happens
>>>>>
>>>>> I'm sure the distro users of msys2 won't mind a performance hit until
>>>>> 3.8 rather then having no support at all.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Aug 5, 2015 at 10:51 PM, Rui Ueyama <ruiu at google.com> wrote:
>>>>>
>>>>>> On Mon, Aug 3, 2015 at 10:36 PM, Martell Malone <
>>>>>> martellmalone at gmail.com> wrote:
>>>>>>
>>>>>>> From my reading on how gnuld handles PE/COFF
>>>>>>> It uses a linker script that describes how it lays out its idata
>>>>>>> section.
>>>>>>> From i386pe.x
>>>>>>>
>>>>>>>   .idata BLOCK(__section_alignment__) :
>>>>>>>   {
>>>>>>>     /* This cannot currently be handled with grouped sections.
>>>>>>> 	See pe.em:sort_sections.  */
>>>>>>>     SORT(*)(.idata$2)
>>>>>>>     SORT(*)(.idata$3)
>>>>>>>     /* These zeroes mark the end of the import list.  */
>>>>>>>     LONG (0); LONG (0); LONG (0); LONG (0); LONG (0);
>>>>>>>     SORT(*)(.idata$4)
>>>>>>>     SORT(*)(.idata$5)
>>>>>>>     SORT(*)(.idata$6)
>>>>>>>     SORT(*)(.idata$7)
>>>>>>>   }
>>>>>>>
>>>>>>>
>>>>>> Yeah, I found that too and it (especially the way how it creates a
>>>>>> gap between .idata$3 and .idata$4) looks really hacky. I also found that
>>>>>> GNU ld has a special logic to order .idata$<n> sections.
>>>>>>
>>>>>> At first I thought that I could mimic GNU ld and MSVC linker to
>>>>>> generate the .idata section, but seems like it would really mess up the DLL
>>>>>> import table generation code. We probably should keep the existing logic.
>>>>>>
>>>>>> I then tried to detect dlltool-style import files and read them as if
>>>>>> they were short import libraries, so that I can keep the existing code.
>>>>>> That didn't work well because it's not easy to detect dlltool-style import
>>>>>> files in a reliable manner without sacrificing performance.
>>>>>>
>>>>>> It feels to me that it makes more sense to add a new option to
>>>>>> dlltool to generate short import libraries. It shouldn't be that hard.
>>>>>> Martell, what do you think?
>>>>>>
>>>>>>> Under ld/emultempl/pep.em in binutils it describes how it converts the MS import library to its format.
>>>>>>> see here http://github.com/bminor/binutils-gdb/blob/master/ld/emultempl/pep.em#L1625
>>>>>>> From the code in this function and the rest of pep.em we can see how it handles it.
>>>>>>> I'm sure this will make more sense to you however as you know what the MS format is.
>>>>>>>
>>>>>>> I assume the conversion will have to go the other way for us
>>>>>>> I think the most notable thing is the use of idata7 instead of idata6 for the dll name
>>>>>>> We could use that as a check?
>>>>>>> Then hijack it pulling out the function names once we see this being used and insert it into the sections like a MS generated one
>>>>>>>
>>>>>>> You might have a much cleaner solution however. :)
>>>>>>>
>>>>>>> If this isn't enough insight into what you need I can do more digging.
>>>>>>> Just ping me and let me know
>>>>>>>
>>>>>>>
>>>>>>> On Tue, Aug 4, 2015 at 3:15 AM, Rui Ueyama <ruiu at google.com> wrote:
>>>>>>>
>>>>>>>> ruiu added a comment.
>>>>>>>>
>>>>>>>> Do you know anything about how GNU ld handles these import
>>>>>>>> libraries? My
>>>>>>>> linker is able to read it and construct .idata section, but the
>>>>>>>> resulting
>>>>>>>> .idata section is not going to be in correct format. If GNU linker
>>>>>>>> is able
>>>>>>>> to generate a correct .idata section from this type of import
>>>>>>>> libraries,
>>>>>>>> there must be something I'm missing in my linker.
>>>>>>>>
>>>>>>>>
>>>>>>>> http://reviews.llvm.org/D11724
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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